Conventional knitting machine cylinders generally include four main parts: a cylinder body, a sinker ring or dial, a top ring, and a plurality of metal inserts. The outer cylindrical face of the cylinder body is typically machined to form spaced-apart, radial slots in which metal inserts are individually positioned. The metal inserts, which typically terminate proximate the upper edge of the cylinder body, extend radially outward beyond the slots to define a trick between each pair of adjacent inserts. These tricks receive the needles of the knitting machine, and act as guides for the vertical reciprocating needle motion.
The top ring is conventionally formed as a separate single element which is secured to the top of the cylinder. Prior to its securement to the cylinder body, the top ring is typically machined so that it includes a plurality of radial slots for receiving the sinkers. This machining process must be very precise, in order that the slots in the top ring will align correctly with the slots in the outer cylindrical face of the cylinder body. Thus, machining of the top ring can be time consuming and expensive.
When the top ring is secured to the top of the knitting machine cylinder, it provides support for lower surfaces of the sinkers, i.e. the bottoms of the sinker pawls, and for the backs of the needles. Because the reciprocating motions of the sinkers and needles generate large amounts of frictional forces along the wear surfaces of the top ring, it can become worn after only a minimal amount of use. Further, the tensional forces exerted by the knitted fabric being drawn down from the machine tend to localize the forces along the top ring, thereby exacerbating the problem of top ring wear.
To counter the effects of these frictional forces and minimize the resultant wear incurred, top rings have historically been heat treated in order to harden them so that they will be more resistant to wear. Heat treatment, however, often results in deformation of the top ring due to expansion, contraction and/or warping of the ring material. As discussed above, the top ring must be precisely shaped in order that it cooperates properly with the cylinder body; thus, deformations resulting from the heat treatment of the top ring must be corrected prior to its use. Correction of such top ring defects is typically expensive and time consuming, and thus can represent a significant cost of knitting machine production and operation. Further, because these prior arrangements require machining and slotting of two individual parts, i.e. the cylinder body and the top ring, manufacture of the machines tends to be relatively slow and expensive. Additionally, because the top ring is typically formed as a single continuous piece, top ring damage or wear, which may occur in a discrete area, usually requires replacement of the entire top ring, though a major portion of the ring is still in usable condition. Further, with conventional machining and heat treating processes, it is often difficult to achieve highly polished surfaces; the resulting rough surfaces are undesirable because they increase the amount of frictional forces produced during the knitting process and contribute to the build up of lint, which can interfere with the function of the machine.
FIGS. 1-3 depict such a typical prior art cylinder assembly for a circular knitting machine, shown generally at 10. The cylinder assembly includes a cylinder body 12, which has a plurality of spaced-apart radially extending walls 14, between which are defined a plurality of slots 16. An insert 18 is positioned within each of the slots 16, with each of the inserts extending outwardly beyond the walls 14 to define needle-receiving channels (commonly referred to as tricks) 20 between adjacent inserts.
A top ring 22 is secured to an upper face of the cylinder body 12, such as by a screw 28 which extends through an opening 30 in the top ring and a threaded opening 32 in the cylinder body. As illustrated, the inserts 18 typically terminate below the top ring 22 such that the top ring assists in their securement to the cylinder body 12.
The top ring 22 includes a plurality of upwardly extending walls 24 along its upper surface, with the walls being spaced apart to define sinker receiving channels 26. As discussed above, the top ring 22 typically provides bearing surfaces for reciprocating needles (not shown) positioned within the tricks 20 and for sinkers (not shown) which extend through the channels 26 on the top ring. Because large amounts of frictional forces tend to be produced by the reciprocating motions of the needles and sinkers, the bearing surfaces tend to wear adversely. Thus the top ring 22 is typically heat treated to harden it so that the ring is better able to withstand such frictional forces and wear is minimized. As illustrated in FIGS. 1-3, the mating engagement of the top ring 22 to the cylinder body 12 must be tight and accurate in order that the moving elements of the knitting machine are properly aligned with the channels in which they reciprocate. Thus, any warping or other deformation which results from the heat treatment must be corrected before the cylinder can be effectively utilized. As a result, the machined, heat treated top ring tends to be expensive to produce and expensive to replace.
Other attempts have been made to overcome the deleterious effects of the frictional forces on the knitting machine cylinder. For example, U.S. Pat. No. 3,230,742 to Roedel describes a replaceable synthetic insert for increasing resistance of the inner sinker ring to frictional wear. A replaceable insert in the form of a ring is bonded by a layer of adhesive to the top of the inner sinker ring. The insert is then machined to provide guides for the sinkers and needles. Because the insert must be machined to define slots for the sinkers, the manufacturer must be particularly exact in slotting the insert in order that it will correspond appropriately to the slots containing the inserts in the outer cylindrical face of the cylinder body. Additionally, because the insert is a continuous circular band, there is no provision for any adjustment in its circumference, and the entire band may require replacement following damage to a single portion thereof.
U.S. Pat. No. 1,952,928 to Lawson describes a needle cylinder, the upper edge of which contains a plurality of grooves in which a plurality of inserts are frictionally engaged. The inserts are described as providing guidance for the horizontal motion of the sinkers and they may be connected by extensions to form sections of a sectional top ring. There is no provision, however, for making the individual inserts resistant to the frictional forces provided by the movement of the sinkers and needles. Similarly, there is no provision for supporting the underside, or pawls, of the sinkers.
U.S. Pat. No. 5,077,990 to Plath describes a friction reducing surface applied to a conventional slotted top ring of a circular knitting machine. Though this top ring is treated to reduce the amount of wear it receives, it requires the formation of slots therein. Thus, when the top ring is replaced, a new top ring must be accurately slotted to match the slots in the outer cylinder body face. Further, because the top ring is formed as a single unit, wear in a discrete area can require replacement of the entire top ring.
Thus, a need exists for a cylinder structure for a knitting machine which can withstand the deleterious effects of the frictional forces produced by the sinker and/or needle movements, which can be readily and easily replaced, and which can be inexpensively fabricated.
Further, a need exists for a cylinder assembly for a circular knitting machine which can be hardened by conventional heat treatment processes and which can allow discrete regions which may become damaged to be replaced without requiring replacement of an entire top ring.
Additionally, a need exists for a cylinder assembly which reduces the amount of frictional forces produced during the knitting operation and the build up of lint on the machine.